ES2247286T3 - DEVICE FOR THE PREPARATION OF THE POSITIONING OF A KNEE PROTESIS. - Google Patents

Abstract

Method for measuring the balance of the ligaments of a knee using a sensor (7) for measurement of a physical value that is proportional to the force developed by the ligaments on a sensor arranged between the two articulation parts of the knee. The sensor is placed between a tibial section and the lower extremity of the femur prior to its resectioning. <??>An Independent claim is made for an ancillary device with a sensor for measuring the forces applied to first and second femoral plates.

Description

Device for the preparation of positioning of a knee prosthesis.

The invention corresponds to a device for procedure for measuring the balance between ligaments and for preparation of the positioning of a knee prosthesis.

The placement of a knee prosthesis presents Several difficulties

The femur and tibia are united by the internal and external ligaments, which should be preserved operate.

Each of these ligaments exerts a force tractor unit that tends to bring the lower end of the femur and the upper end of the tibia, and in the same way, to maintain a Preferred orientation for the tibia and femur.

The forces developed by these ligaments they also depend on the angular position of the tibia with regarding the femur as to whether the limb is flexed or extended.

According to each individual, it is established of naturally a balance of forces exerted by ligaments, called the balance between ligaments, and it is important respect it.

It is necessary then to be able to respect the balance between ligaments, while preventing tension from the ligaments after prosthesis positioning be too loose or too strong regarding the situation initial.

Currently:

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during the operation the tense surgeon ligaments by means of a tensioner or tweezers, called apartadores, to separate the two parts of the joint to then proceed to resection the parts of the femur and the bone tibia; Y

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by means of measuring ligament lengthening, and its medical experience, the surgeon aims to reach balance between ligaments

If the positioning operation of this prosthesis does not sufficiently respect this balance between ligaments, then there are numerous dislikes for the patient.

A measuring device of a ligament balance (US-5,470,354, WO-92/17113 and US-5,656,785) which,  after placement of the two parts of the prosthesis knee, consists of inserting between the two parts of the prosthesis a measuring device to determine this balance between ligaments, and by then adapt the morphology of the prosthesis.

To use this device it is necessary have prostheses with adjustment means, which increases the cost of the prostheses.

If adjustable prostheses are not available, it is you need to cut the tibial part again, or make a rotation in the plane of support of the femur.

Another problem arises with the positioning of the resection cuts.

Indeed, the tibial cut must be made perpendicular to the mechanical axis of the tibia, an axis often confused with the spinal axis.

The same goes for the femur, although this axis mechanic is normally inclined a few degrees, between 3rd and 11th, with respect to the anatomical axis of the femur.

The surgeon usually uses the plates flat radiographs to determine the theoretical cuts, since positions, by means of anatomical reference points, the dimensions of the cut.

Start with the tibial cut where the thickness does not must be less than the default value, for example eight millimeters

Here too the surgeon's experience is paramount when determining the cut.

In effect, the surgeon must remove the part of the damaged joint, while retaining the largest part possible healthy joint.

It is then understood that what determines the cut depends largely on the experience of the surgeon, and not of the controlled physical parameters, and that the choice of cut influences the balance between ligaments.

The object of the invention is to solve such inconvenience

US-A-5,213,112 presents a device according to the preamble of the Claim 1.

The inconveniences above are solved mentioned by means of a device as defined in the Claim 1.

To better understand the invention in the description mentioned below, included by way of non-limiting example, and in accordance with the accompanying drawings they represent, schematically
AC:

- Figure 1: a front view of a joint before resection;

- Figure 2: the joint after tibial saucer resection;

- Figure 3: the positioned device;

- Figure 4: a top view of the device of Figure 3;

- Figures 5 and 6: different devices, of according to the invention.

With reference to the drawing, you can see a knee joint (1).

Such articulation is composed of two parts, it is say a top part (2) that is the base of the femur, and a part upper (3) which is the upper end of the tibia.

These two parts of the joint are joined by an external ligament (4) and an internal ligament (5).

Each of these two ligaments exerts a tensile force that establishes a balance between ligaments.

To place a knee prosthesis, you start for defining the tibial cut (6) and normally some cutting dimensions (not shown) to perform such cut.

To define the cut, the leg is reconstructed of the patient in three dimensions and, with a calculator, Determine the position of the tibial cut.

After having resected the tibial saucer, the measuring device is inserted into the tibial cut to measure the balance between ligaments, both in flexed position as in the extended leg position.

Advantageously, the device for Preparation of the positioning of a knee prosthesis makes up at least one measuring device (7) of physical size proportional to the strength developed by the ligaments on the device arranged between the two parts of the joint.

After taking the measurements, they are introduced the values again in a calculator to determine the position and the orientation of the femoral cut, according to the morphology of The prosthesis and the patient.

This allows us to guarantee the conservation of natural balance between ligaments.

An embodiment of the invention has a device consisting of a support (8) provided with apparatus for pressure collection (7A), to position between the tibial cut and the lower end of the femur.

The support, positioned on the tibial cut, is Presents in the form of a plate that rests on the tibial cut, with the collection devices (7A) located on the upper face.

By measuring the pressure exerted both when extending the limb and flexing it, you can establish balance between ligaments.

Pressure capture devices are connected to a device (9) for displaying the measurements.

It is possible to use the collection devices of mechanical or piezoresistive type pressure.

In reference to the collection devices mechanical, are the pressure capture devices by manometer.

The principle of operation is as follows: a curved metal tube communicates with the enclosure where it find the gas with which the measurement of the Pressure.

One of the extremes, the "entrance", is permanent; The second is free. Under the effect of pressure the tube it deforms and the free end moves.

Since the end of the tube is attached (by means of a gear mechanism) to a needle, when deforming it You can read the pressure.

Similarly, this tube can be replaced by a membrane that travels as a function of pressure. Membrane It is attached to a needle by means of a mechanism.

The advantage of using this collection device It is the simplicity of use.

Indeed, no external link is necessary (unlike an extensiometric gauge) since it works as autonomous way. In addition, since pressure is a linear function of the force applied to the cat, the conversion of A pressure on a force.

For this reason, it is enough to graduate the sphere in Newton when converting. And finally, and since the system is fully mechanized, it is possible to find a device resistant to severe conditions (135ºC, 100% humidity).

Instead, the volume of the extender

Regarding the collection devices formed by a piezoresistive membrane, this type of device measures the deformation of a part of the enclosure, by enclosing the fluid with the which can be done the pressure measurement.

A caliper can be positioned on the deforming membrane. The hard part is measuring these deformations On a small surface. However, there are manufacturers that produce miniature pressure sensing devices that they would agree with the study chart.

In this case, these are devices provided of piezoresistive membranes, whose resistance varies depending on the deformity It would be enough to position a pickup device inside each of the cats to be able to measure the pressure.

Compared to the previous one, the advantage of this type of collection apparatus is that it is less bulky (at least in the operating room).

Instead, you need a complete team in the outside the enclosure (food, acquisition of measures). The reading is easier (since in most cases it is about a digital display). Instead, you can perform this display only outside the enclosure.

In another variant of the invention, the tensioner is used (10) to take this measurement, used to separate the two parts of the joint

The tensioner is composed of a davit (11) and a femoral shoe (12).

In a first variant of the invention (Figure 5), add a second second over the femoral shoe (12) Femoral shoe (13) that moves freely through the davit, and positions a force pickup device (7B) between the shoe existing femoral and the second.

In this way, the device is composed of a force pick-up apparatus (7B), arranged between a shoe femoral (12) rigidly fixed to a davit, and a second Femoral shoe (13) that slides through said davit.

Then a part of the davit constitutes a rail (14) for the mobile femoral shoe.

For reasons of volume, the femoral shoes are of a reduced thickness.

In another variant of the invention (Figure 6), the tensioner (10) is composed of a davit (11) and a shoe femoral (12), and presents, on both sides of the davit, a force gauge (7C) to know the level of the extended fiber and compressed fiber. This allows you to free yourself from the point of application of force on the shoe and the section of the shoe.

The davit has grooves (14) located at the level of the extended and compressed fibers, in order to position the force gauges and the threads that bind them to the measuring device
gives.

As indicated above, the device allows to preserve the balance between ligaments by means of accurate measurement of ligament traction.

A shoe can be seen in Figure 6 tibial (16) and the femoral part fixed in the davit.

A systems expert will analyze the values marked by calipers.

Claims (4)

1. A device for preparing the positioning of a knee prosthesis, consisting of a femoral shoe (12) rigidly fixed on a davit (11), and a second femoral shoe (13) that slides by said davit, characterized by the fact that it is composed of at least one force pick-up apparatus (7B), arranged between the fixed shoe and the mobile shoe. 2. A device for preparing the positioning of a knee prosthesis according to Claim 1 characterized in that a part of the davit constitutes a rail (14) for the mobile femoral shoe. 3. A device for preparing the positioning of a knee prosthesis composed of a tensioner (10) with a davit (11) and a femoral shoe (12), characterized by the fact that it presents, on both sides of the davit, a caliper (7C) of force to know the level of the extended fiber and the compressed fiber. 4. A device for preparing the positioning of a knee prosthesis according to Claim 3 characterized in that the davit has grooves (14) located at the level of the extended and compressed fibers, in order to position the calipers of force and the threads that bind them to the measurement display device.